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Studies on the influence of bacteria and carbon source on the products of dissimilatory iron reduction

STUDIES ON THE INFLUENCE OF BACTERIA AND CARBON SOURCE ON
THE PRODUCTS OF DISSIMILATORY IRON REDUCTION
by
Everett Cossio Salas
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfi llment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)
December 2008
Copyright 2008 Everett Cossio Salas

The aim of my work is to elucidate the interactions between microbes and minerals. The work I present here describes studies I have done investigating factors that can influence the identity of reduced iron oxide minerals.; There is no doubt that microbes play an important role in the redox cycling of iron oxides in soils and sediments. The microbially mediated reduction of iron oxides can lead to the remobilization of iron as well as the formation of reduced iron minerals. Beyond acting as a source of Fe2+, the bacteria themselves are thought not to play a role with respect to the nature of the resulting reduced iron minerals. Several factors, such as the carbon substrate used for energy, the strain of bacteria used in experiments and the rates at which the bacteria reduced iron, were investigated under laboratory conditions to determine their importance in iron mineral formation.; Shewanella putrefaciens CN32, Shewanella putrefaciens W3-18-1 and Shewanella oneidensis MR-4 all produced magnetite when given lactate as the carbon source. However, they differed in the amount of magnetite each produced. Strain W3-18-1 also produced a mixture of magnetite and iron carbonate hydroxide, although most of the reduced iron remained in an amorphous phase. When strain W3-18-1 was given pyruvate, the major biomineral was siderite, while incubations with uridine produced pure iron carbonate hydroxide. Although the bacteria reduced iron at comparable rates, the products of this reduction were all quite different, suggesting that rate, while important, is not the primary determinant in what phases of iron minerals will be produced in laboratory studies.; The results presented here suggest that chemistry appears to be the important factor in determining the identity of the resultant iron minerals. However, the chemistry itself was extensively altered by the metabolic activity of the bacteria, making them much instrumental to iron mineral formation than merely acting as a source of reduced iron.

STUDIES ON THE INFLUENCE OF BACTERIA AND CARBON SOURCE ON
THE PRODUCTS OF DISSIMILATORY IRON REDUCTION
by
Everett Cossio Salas
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfi llment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)
December 2008
Copyright 2008 Everett Cossio Salas